We propose a collaborative case-control study to identify and evaluate risk factors for multiple myeloma and chronic lymphocytic leukemia. Cases of these diseases will be identified through population-based cancer registries in Washington State, Utah, Detroit and Atlanta, over a three-year period. Control subjects will be identified from the general populations from which the cancer cases arose. Probability sampling methods, such as area sampling and random digit dialing, will be used for selection of controls. Cases and controls will be interviewed with particular attention to variables related to chronic antigenic stimulation, e.g., past illnesses, allergies, drugs, etc. We will also obtain detailed residence and occupational information in an attempt to generate new etiologic hypotheses.